In the use of plastic beverage closures on glass or plastic containers, it is essential to provide a proper seal for the carbonated beverages in the glass or plastic containers. In addition, it is essential to be able to vent the pressure of the contents as the closure is being unthreaded and before the threads become disengaged in order to facilitate the opening of the contents. In order to vent the contents, the seal must first be released.
In order to provide a proper seal, it has been thought that it is necessary to have a seal on the top surface of the container as well as on the outer cylindrical surface of the finish or neck of the container. Thus, in compression mold liners a satisfactory seal has been provided as shown in, for example, U.S. Pat. Nos. 4,378,893, 4,407,422 and 4,418,828 incorporated herein by reference. In these patents, the closure is provided with an annular lip spaced from the base wall and defining an annular recess and a plastic sealing liner in compression molded such that it is held in position by integral liner-engaging projections on the base wall and the annular lip to form a liner that has an annular sealing bead that engages the outer side wall surface of the container. In another type of plastic beverage closure shown in U.S. Pat. Nos. 4,462,502 and 4,658,976, a circular flexible resilient liner is provided which is rotatable relative to the closure and has a diameter greater than the outside diameter of the container lip. An annular projection is provided at the juncture of the base wall and skirt of the closure and preferably has a configuration when viewed in cross-section which has a horizontal portion, a vertical and a convex portion connecting the horizontal and vertical portion one to the other providing for sealing along an outer cylindrical side surface of the edge of the finish of the container.
In each of the aforementioned constructions, the construction relies on the flexing of the base wall of the closure to enhance the side seal on the cylindrical surface of the container finish.
It has also been found that the nature of the seal provided is such that venting does not occur until a rotation of about 90.degree.-120.degree. of the closure occurs.
Among the objectives of the present invention are to provide a plastic beverage closure which has a seal which will effectively protect the contents of the container which may be under pressure; wherein the closure effectively vents any pressure of the container with a minimal rotation of the closure; which the closure is operable on both glass and plastic containers; wherein the liner material may be of a broad range of materials; which does not require an annular lip on the closure for retaining the sealing liner that might interfere with either the glass or plastic container finish; and which does not rely on a seal with the outer cylindrical surface of the finish of the container.
In accordance with the invention a plastic beverage closure comprising a base wall, a peripheral skirt and a plurality of threads on the inner surface of the skirt for engagement with the threads of a container which may be made of glass or plastic. The plastic closure includes a compression molded seal extending about the periphery of the inner surface of the base wall and the juncture of the base wall to the peripheral skirt. The closure includes a central axially thickened portion; a channel surrounding the thickened portion and extending radially to an annular radially thickened portion on the skirt at the juncture with the base wall. A concave surface extends from the base of the channel and merges with the surface of the annular portion. A compression molded liner is provided on the thickened portion, channel and concave surface of the closure and defines a planar sealing surface for contact with the end surface of the finish of the container and an arcuate surface for engaging the arcuate surface of a container.